An ECS container instance is an EC2 instance that’s:
- running Amazon’s ECS container agent and
- has been registered into a cluster
- the container agent is automatically installed if you’re using an Amazon ECS-optimized AMI
- the agent will make API calls to Amazon ECS so the instances will need an IAM role
For more on this see:
Note, however, if you’re using Fargate this does not apply (see docs).